1. Field of the Invention
The present invention relates to an apparatus for storing data including audio and/or video (AV) data and for transmitting them, suitable for being applied to an AV server device for storing and reproducing AV data etc. More specifically, the invention relates to an apparatus making it possible to construct a data processing system in which real time control can easily be carried out and excellent responsivity can be exhibited, by connecting an receiving buffer unit for storing temporarily AV data etc., an transmitting buffer unit for transmitting AV data etc. and the like unit by means of a network means.
2. Description of the Prior Art
A structure shown in FIG. 22 is known as an AV server device which is a type of an apparatus for storing AV data etc., and for transmitting the desired AV data at real time.
In the FIG. 22, a HDD (Hard Disk Drive) array unit 12 (which will be referred to as a disk array unit, hereinafter) having such an array structure that a plurality of hard disk drives are connected in parallel with each other is provided for using as a storage means for storing AV data, and this disk array unit 12 is connected to an internal bus 16 through an SCSI interface 14.
To the internal bus 16, a receiving interface 20 for AV data supplied from a terminal 18 is connected so that the received AV data are stored in the disk array unit 12, and thereto an transmitting interface 22 is connected through the internal bus 16 so that the reproduced AV data are transmitted from a transmitting terminal 24.
A control signal interface 28 for a real time control through a terminal 26 is also connected to the internal bus 16.
As the control signal, the following can be taken into consideration: a signal transmitted from an editing unit (not shown) connected to an AV server device 10, a signal synchronized with sending-out-timing signal transmitted from a program sending-out unit (not shown) disposed in connection with an application terminal 36 in case where this AV server device 10 is illustratively applied to a commercial sending-out system.
Furthermore, the followings are connected to this internal bus 16: a CPU 30 for controlling the whole of the AV server device, a ROM 32 including various control programs, and a RAM 34 for storing, for example, file control information for AV data stored in the disk array unit 12. In addition to this, in this example, to the internal bus 16 a network interface 40 is connected, and the present AV server device is connected to the outer application terminal 36 (terminal equipment such as a workstation or a personal computer) from this network interface 40 through a network 38.
Reproducing operations for AV data stored in the AV server device are illustratively explained hereinafter.
Firstly, the application terminal 36 sends a file information acquiring command to the AV server device 10 through the network 38. Said file information acquiring command orders the indication of the information relating to the file storing the AV data to be reproduced. Next, CPU 30 of the AV server device 10 transfers the file information stored in RAM 34 therefrom to the application terminal 36 in response to the file information acquiring command received from the application terminal 36.
Then, the application terminal 36 sends to the AV server device 10 a file open command that is a command to operate the file storing AV data to be reproduced on basis of the received file information. The CPU 30 of the AV server device 10 reads out the file information stored in the RAM 34 on the basis of the received file open command and waits for a next command from the application terminal 36. Next, the application terminal 36 issues to the AV server device 10 a reproducing command relating to the file received the file open command. The CPU 30 of the AV server device 10 receives said reproducing command and issues a reproducing command relating to the file to be reproduced to the disk array unit 12 through SCSI interface 14 according to the read out file information. The disk array unit 12 receives said reproducing command and allows the hard disk drive inside the unit 12 to be accessed. Thereby, the AV data are reproduced from the area where said file to be reproduced is stored in hard disk of the hard disk drives and the reproduced AV data are transferred to the internal bus 16 through the SCSI interface 14. The CPU 30 controls the internal bus 16 so that the AV data transferred into the internal bus 16 are transmitted to the transmitting interface 22. Said CPU 30, thus, transmits the AV data to the outside via the transmitting interface 22.
In the above AV server device 10, all of the receiving interface 20, the SCSI interface 14 and the transmitting interface 22 are connected to the internal bus 16, and the CPU 30 controls all of them. All of the AV data are stored in the disk array device 12. Thus, there remain the following problems.
Firstly, the number of the receiving and transmitting channels is limited by a transfer rate at the internal bus. This is because the receiving interface 20 and the transmitting interface 22 are directly connected to the internal bus 16 and consequently the number of the receiving and transmitting channels is limited by a restriction to hardware (a transfer rate at the internal bus).
For example, when the transfer rate at the internal bus 16 is 20 Mbyte/sec (=160 Mbps), the total number of the receiving and transmitting channels is 8 at maximum in case where the compression rate for AV data is 20 Mbps.
Secondly, since the receiving interface 20 and the transmitting interface 22 are directly connected to the internal bus 16, it is impossible to arrange receiving means, transmitting means, storage means, and the like in a physically separate form. Thus, a design for construction of an AV server system is restricted.
Thirdly, the reliability of the disk array unit 12 deteriorates since the disk array unit 12 is controlled at real time in recording/reproducing AV data. For example, it will be assumed that in case where a plurality of the transmitting interfaces 22 exist, these plural transmitting interfaces are simultaneously operated.
In order that transmitting AV data from the respective transmitting interfaces are not interrupted, it is necessary that a specified amount of data reach each of the transmitting interfaces within a specified period. This requires real time reading about reading data in the hard disk.
In hard disks, seek time and rotation-waiting time vary depending on the position of a head. Therefore, in order to reproduce AV data without interruption, it is necessary that seek time and rotation waiting time are set to the worst value. To obtain a transfer rate necessary for this, it is necessary to provide many hard disks and operate these disks in parallel.
The reliability of a hard disk is obtained on the basis of retry processing of the access to the hard disk. Therefore, when the retry number for a hard disk is limited to a minimum number (10 or less in usual cases), the error rate is deteriorated from 100 to 1000 times. Where hard disks are arrayed and real time reading is required, the retry number for the hard disks has no choice but to be limited. As a result, the reliability as a disk array unit drops.
Fourthly, to increase storage capacity, only addition of the disk array units 12 is permissible. When a tape device (a tape changer device using many magnetic tapes, or the like), which is low-priced for capacity, attempts to be used because of a high price of a hard disk drive, this tape changer must also be connected to the internal bus 16. As a result, transfer capacity of the internal bus 16 is further consumed, so that the number of receiving and transmitting channels, which can be handled, is reduced for that.
Fifthly, the period from the arrival of a file open command from the application terminal 36 to the reproduction of the file to be reproduced is decided by access time to the hard disk drive. Since this period is substantially decided by the maximum value (several ten msec.) of seek time and rotation waiting time of the hard disk drive, the responsivity of the AV server 10 is decided by the performance of the hard disk drive itself. As a result, a high-speed responsivity thereof cannot be expected so far as the hard disk drive is used.
Thus, this invention solves these problems in the prior art, and it is an object of this invention to provide an apparatus for storing and transmitting data, which can be illustratively applied to an AV server device, the apparatus making it possible to construct an AV server system or the like which can make real time control easy and have excellent responsivity. To solve the aforementioned problems, the present invention provides preferably an apparatus for storing and transmitting data comprising a first storage means for storing the AV data received from the outside, a second storage means for storing said AV data, a data transmitting means for storing temporarily said AV data and transmitting them to the outside, and a main control means for controlling said data transmitting means, said first storage means and said second storage means. In this invention, said network means links each of said data transmitting means, said first storage means and said second storage means. Since the number of receiving and transmitting channels is decided by the network means itself, the number more than the one of the prior art can be kept sufficiently in the present invention. It is not feared that it is limited by capacity of the internal bus. Each of said data transmitting means, said first storage means and said second storage means can be arranged discretely because their physical arrangement or distances are not limited.
Since data transfer, in this invention, among the first and second storage means and the data transmitting means, is implemented as communication on an ordinary network and the data are reproduced at real time from the transmitting means, real time processing between the storage means and the transmitting means is not required.
Therefore, this makes it possible to take measures for keeping reliability of the storage means sufficiently, and consequently, for example, in case where a disk array unit or the like is used, the number of retry thereto can be set a larger value. This makes it possible to improve reliability of the disk array unit to a large extent.
Furthermore, in this invention, a data transmitting means stores temporarily said data and the stored data are transmitted to the outside by the reproducing command and thus, the responsivity to the reproducing command can be improved to a large extent.
In the present invention, the main control means controls said data transmitting means, said first storage means and said second storage means so that said second storage means stores at least said data stored temporarily in the transmitting means and said first storage means stores at least said data stored in the second storage means. This makes the data hierarchikal.
According to the present invention, an AV server device having large capacity and good responsivity can be constructed with good cost balance. Further, according to this structure, even if hard disk units are used as the storage means, real time processing to hard disk units is not required.
A method for storing and transmitting data of this invention includes preferably the steps of: storing said data received from the outside in said data storage means; transferring said data from the data storage means to said data transmitting means through said network means by deleting specified data stored previously in said data transmitting means therefrom when the stored data are transferred to said transmitting means where the transmitting means has less capacity than that is needed for storing said transferred data; and storing temporarily said transferred data in said data transmitting means.
Further, the storage means of the apparatus of this invention may be composed of only one storage means. In this case, this apparatus may be used in the broadcasting station where there is only a relatively small area for installing it.
A further understanding of the nature and advantages of the invention may be realized by reference to the following portions of the specification and drawings.